Refactor processing logic and enhance error handling

- Cleaned up code in processing.py by removing inline semicolons and improving readability.
- Updated upsert_file_relation calls to ensure consistent handling of file relations.
- Enhanced query_file_relations in db_schema.py to support filtering by file existence.
- Improved API error handling in index.ts with user-friendly messages for 401 and 403 errors.
- Added online/offline status tracking in Layout.vue.
- Implemented debounced search functionality across multiple views to optimize performance.
- Introduced loading skeletons in Dashboard.vue for better user experience during data fetching.
- Enhanced file preview cleanup logic in Images.vue, Orders.vue, and Tables.vue to prevent memory leaks.
- Updated global styles to include new loading and notification animations.

web/frontend/src/views/files/Tables.vue

@@ -85,7 +85,7 @@
       </el-table-column>
     </el-table>
 
-    <el-dialog v-model="showPreview" title="文件预览" :fullscreen="true" append-to-body :close-on-click-modal="false" class="preview-dialog">
+    <el-dialog v-model="showPreview" title="文件预览" :fullscreen="true" append-to-body :close-on-click-modal="false" class="preview-dialog" @close="cleanupPreview">
       <div class="preview-body">
         <div v-if="previewType === 'image'" class="preview-image-wrap"><img :src="previewSrc" style="max-width:100%;max-height:100%;object-fit:contain" /></div>
         <div v-else-if="previewType === 'excel'" class="preview-table-wrap"><table class="preview-table"><tr v-for="(row, ri) in previewRows" :key="ri"><td v-for="(cell, ci) in row" :key="ci">{{ cell }}</td></tr></table></div>
@@ -125,7 +125,7 @@ const items = ref<any[]>([])
 const total = ref(0)
 const page = ref(1)
 const pageSize = 50
-const loading = ref(false)
+const loading = ref(true)
 const selected = ref<any[]>([])
 const sortBy = ref('created_at')
 const sortOrder = ref('desc')
@@ -183,6 +183,15 @@ async function previewFile(row: any) {
   } catch { ElMessage.error('预览失败') }
 }
 
+function cleanupPreview() {
+  if (previewSrc.value && previewSrc.value.startsWith('blob:')) {
+    URL.revokeObjectURL(previewSrc.value)
+  }
+  previewSrc.value = ''
+  previewType.value = ''
+  previewRows.value = []
+}
+
 function showDetail(row: any) {
   const fname = row.output_excel || row.result_purchase || row.input_image
   const stem = fname.replace(/\.[^.]+$/, '')